Radio Frequency Identification (RFID) is a technology that incorporates the use of electromagnetic or electrostatic coupling in the radio frequency portion of the electromagnetic spectrum to uniquely identify an object, animal, or person. RFID is used as an alternative to the bar code technology. An RFID system consists of three components: an antenna, a transceiver, and a transponder (the tag). The antenna and transceiver are often combined into a single reader. The antenna uses radio frequency waves to transmit a signal that activates the transponder. When activated, the RFID tag transmits data back to the antenna. The data is used to notify a programmable logic controller that an action should occur. The action could be as simple as raising an access gate or as complicated as interfacing with a database to carry out a monetary transaction. Some tags can be read from several meters away and beyond the line of sight of the reader.
RFID tags come in three general varieties: passive, active, or semi-passive. Passive tags require no internal power source, thus being pure passive devices (they are only active when a reader is nearby to power them), whereas semi-passive and active tags require a power source, usually a small battery. Depending on the attachment with identified objects, the tags can be attachable, implantable, and inserted.
RFID technology is widely used in many application fields. One important area is Supply Chain Management (SCM) where RFID tags are used to identify and track goods and raw materials along the supply chain. For the efficient organization of the supply chain, identification technologies whose acquisition rate lies close to 100% are needed. Otherwise, the danger exists that systems collect incomplete or faulty data. Although the read range and reading speed of RFID readers have improved in recent years, their reliability is still a problem. The accuracy of bulk capturing (e.g., the reading of a palette of RFID-tagged products) is not satisfying. Poor reading rates of 30% to 90% are common in these applications.
Standard approaches to improve the reliability of RFID systems try to optimize the technologies and protocols used. Many factors, like the frequencies used and the design of the antennas on the tags, influence the performance of the systems and must be optimally adjusted. To avoid interferences and perturbations from simultaneously transmitting RFID tags, multiplexing techniques are used. This can include time multiplexing methods (e.g., time division multiplexing) as well as frequency multiplexing. The latter requires the use of more expensive multi-frequency readers.
Error correcting codes and the Reed Solomon (RS) code are widely used in a variety of error correcting applications. CDs and DVDs use an interleaved RS code to correct errors caused by scratches on the surface. Many data transmission technologies, such as DSL, ATM, and WiMAX, as well as digital broadcast protocols such as Digital Video Broadcasting (DVB) and Digital Audio Broadcasting (DAB), use variants of the RS code to forward error correction.
Several advanced 2D-barcodes that can store more information than the typical linear ones use RS-codes as well. It is applied to single barcodes to make the reading fail-safe and to correct errors caused by damaged or unclear barcodes.
The commonly used RFID standards use error detecting codes such as Cycling Redundancy Checks (CRC). CRC-checksums are calculated over the data stored on a single chip and allow detecting errors caused by a faulty data transmission.
Another example of error correcting codes is the BCH codes. The BCH codes are characterized with the ease with which they can be decoded via an algebraic method known as syndrome decoding. This allows very simple electronic hardware to perform the decoding. The device itself can be small and low-powered. The BCH code is a multilevel, cyclic, error-correcting, digital code used to correct multiple random error patterns.
Hamming code is a linear error-correcting code that can detect and correct single-bit errors. Because of the simplicity of Hamming codes, they are widely used in computer memory (RAM). If more error-correcting bits are included with a message, and if those bits can be arranged such that different incorrect bits produce different error results, then bad bits could be identified. In a 7-bit message, there are seven possible single bit errors, so three error control bits could potentially specify not only that an error occurred but also which bit caused the error.
It should be appreciated that there are many error-correcting codes and the RS codes, BCH codes, and Hamming codes are provided only as examples of such codes.